You can purchase Salted Seaweed Stems at your local asian grocery store but before you use them you need to prepare them.

Salted Seaweed Stems (미역줄기) are sold covered in salt that must be removed.

How to Clean Salted Seaweed Stems (Miyeok Julgi 미역줄기) Before Cooking

Remove the salted seaweed stems from the bag.
Fill a bowl with water until the seaweed stems are completely submerged.
Shake/gently massage the seaweed stems in the water to remove excess salt thoroughly.
Dump out the water and repeat this process 3 times.
Now add fresh water and let the seaweed stems soak for at least 30 minutes.
Strain the seaweed stems and wash once more.
Squeeze out excess water from the seaweed stems.
Now it is ready to be cut into bite-sized pieces and cooked.